The plastic containers made on blow molding machines have substantially greater strength for their weight if the plastic material is stretched biaxially while at orientation temperature.
This invention provides time for a parison on a core rod to come to a uniform temperature throughout the full wall thickness and provides method for stretching the plastic lengthwise of the container and stretching it also circumferentially to obtain biaxial orientation.
A novel feature of the apparatus is the provision of two indexing heads which carry different sets of core rods; and the transfer of parisons from core rods of the first indexing head to other core rods of the second indexing head while the parisons are at elevated temperatures.
Parisons are stripped from core rods and moved into recesses of a transfer device which turns the parisons through an angle of 180.degree. so that the open end of the parison can be applied to an aligned core rod of a second indexing head.
Other objects and advantages of the invention will appear or be pointed out as the description proceeds.